If you don’t deplete the UFO’s lifebar in time, when there are like 2 seconds left, the UFO will ascend and will fly away with all your collected points.
The big UFO will start ascending when a midboss appears even if it has more than 2 seconds left on its timer.
The big UFO will be destroyed when the boss dialogue appears.
If you have a big UFO on screen and you collect a small UFO, the small UFO will not be lost, but converted into ‘Value’ points.
Be careful! Big UFOs will kill you if you ram into them. So don’t do this.